The act of one's head completing a full 360 degree turn, then vomiting. The original 360 vomit was from the 1973 movie, The Exorcist, where a little girl posessed by the devil himself executed an admirable 360 vomit.

Priests: The power of Christ compells you! The power of Christ compells you!
Posessed Child: BLAAAARRRG *360 vomits*